1. Field of the Invention
The present invention relates to an image pickup apparatus that is capable of taking high-resolution moving images such as high-definition moving images.
2. Description of the Related Art
With regard to image pickup apparatuses capable of taking high-definition moving images, there is a growing need for increased resolution and operation speed in taking still images and moving images. However, the increases in resolution and operation speed would result in an increase in power consumption of an image pickup apparatus, and it is thus difficult to increase recordable time and the number of still images taken due to heat generation of the apparatus and limitations on a capacity of a battery.
Referring to FIGS. 7 and 8, a description will be given of an exemplary conventional image pickup apparatus capable of taking high-definition moving images.
Referring to FIG. 7, an image pickup device 101 produces outputs in a four-channel split output form. AFEs 103 convert analog video signals of respective channels outputted from the image pickup device 101 into respective digital image signals.
For readout at a resolution and a frame rate that can realize high-definition moving image quality, an extremely high operation clock frequency is required. To lower a readout operation frequency per channel to a readout speed that can be realized by the image pickup device 101 with respect to the operation clock frequency that is increased to realize the high-definition moving image quality, the image pickup device 101 produces outputs in the four-channel split output form.
DFEs 104 are digital signal processing circuits that receive outputs from the AFEs 103 and correct for FTN (fixed pattern noise such as line scratches and distortions) included in the outputs from the image pickup device 101. Each of the outputs from the AFEs 103 and the DFEs 104 is a 10-bit parallel digital output.
PS circuits (parallel-serial conversion circuits) 105 convert the 10-bit parallel digital outputs from the DFEs 104 into respective serial digital signals, and outputs the same at low voltage in a differential manner.
An engine 116 receive the outputs of the respective channels from the PS circuits 105, and integrates and combines the split image pickup signals to create a file such as a still image or a moving image in such a form as to be transferred to and from a computer and generate a video signal that can be displayed on a display unit or the like.
A TG (timing generator) 102 generates pulses that synchronize and drive the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, and the engine 116.
A CPU 115 controls operation of the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, the engine 116, and the TG 102 using a control signal 117.
FIG. 8 is a diagram useful in explaining operation timing in a case where recording of a moving image is carried out, and a case where a live view display of a subject is produced in the image pickup apparatus shown in FIG. 7.
In the case where recording of a moving image is carried out, the CPU 115 instructs the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, the engine 116, and the TG 102 to make a transition to a moving image recording operation mode using the control signal 117.
Upon making a transition to the moving image recording operation mode, the TG 102 generates a vertical synchronization signal VD at a speed of 60 fps (60 times per second). In accordance with a control signal 118 including the vertical synchronization signal VD generated by the TG 102, the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, and the engine 116 read out and process field image signals of 60 frames per second in synchronization with the vertical synchronization signal VD. Here, it is assumed that image signals of one field constitute one frame.
On the other hand, in the case where a live view display is produced, the CPU 101 instructs the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, the engine 116, and the TG 102 to make a transition to a live view operation mode using the control signal 117.
Upon making a transition to the live view operation mode, the TG 102 reduces the speed of the vertical synchronization signal VD to a speed of 30 fps (30 times per second) by changing the operation clock frequency to a half frequency as compared with that in the moving image recording mode.
The image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, and the engine 116 read out and process field image signals of 30 frames per second in synchronization with the vertical synchronization signal VD.
In the above described way, in the live view operation mode of which continuous operating time is the longest, power consumption is reduced by switching the operation clock frequency to a half frequency as compared with that in the moving image recording mode so that the heat generation of the apparatus as a whole and the consumption of a battery can be reduced.
However, in blocks that handle analog signals such as the image pickup device 101 and the AFEs 103, there is a large proportion of electric circuits that constantly consume electrical power such as bias electric current irrespective of operation clock frequency. For this reason, even when the operation clock frequency is reduced to half in the live view operation mode, power consumption of the main body of the apparatus is not reduced to half, but is only reduced by about 15% under normal conditions.
Moreover, because the image pickup apparatus has become to use four channels so as to take high-definition images, an apparatus scale required for parallel processing quadruples, resulting in a considerable increase in power consumption, while the percentage of power consumption by the analog signal processing blocks is gradually increasing.
On the other hand, there has been proposed a technique to reduce power consumption of an image pickup apparatus by intermittently driving the image pickup apparatus according to a frame rate required for transmission (Japanese Laid-Open Patent Publication (Kokai) No. H11-168770).
It can be considered to reduce power consumption of the image pickup apparatus in the live view operation mode by intermittently shutting off power to the analog signal processing blocks such as the image pickup device 101 and the AFEs 103 using the above technique described in Japanese Laid-Open Patent Publication (Kokai) No. H11-168770.
However, because of limitations on communication speed, it is technically difficult for the CPU 115 to provide operation mode switching control and electrical power control for the image pickup device 101, the AFEs 103, the DFEs 104, the PS circuits 105, the engine 116, and the TG 102 on a frame-by-frame basis at high speed.